This invention relates to wide band, in-line, microwave amplifiers having a high gain and more particularly to such amplifiers using tetrode or triode vacuum tubes as the active element.
Tetrode and triode microwave amplifiers have two outstanding advantages over other amplifier types for high power applications such as use in a microwave transmitter:
1. PHASE STABILITY AND LINEARITY
2. ECONOMY Likewise, tetrode and triode amplifiers suffer two major limitations:
1. LOW GAIN-BANDWIDTH PRODUCT
2. HIGH POWER NOT CONSISTENT WITH HIGH FREQUENCY. The phase stability and linearity of these amplifiers is a direct result of the short electrical length of the tetrode or triode vacuum tube used as the active element therein. The inherent economic advantage results from the absence of any magnetic field and the fact that the tuned circuitry of the vacuum tube is external to the tube. This allows replacement of the active portion of the amplifier without the necessity of discarding the tuned circuit. Also, since the tube does not contain any internal tuning mechanism, it automatically is a much more versatile device and thus has other potential economic advantages.
An amplifier of the type described which permits in-line use of the amplifier has the further advantage of being easily interposed in the transmission line between the transmitter and the load, which in the case of a phased array radar is an antenna element. This in-line arrangement is convenient and economical as to space.
In view of the inherent advantages of tetrode and triode microwave amplifiers over other amplifier devices, it is not surprising that efforts have been made to improve their performance with regard to gain-bandwidth product and power-frequency limitations. These have included attempts to increase the transconductance of the vacuum tube or to decrease the shunt output capacitance in order to improve the figure of merit of the device. Distributed amplifiers have also been developed in which part or all of the output capacitance is employed in an artificial delay to improve the gain-bandwidth product.